The Omicron variant replaced the Delta variant as the dominant COVID-19 variant in the world, starting from late 2021 to early 2022. But, the SARS-CoV-2 Omicron variant caused less severe disease than Delta, although it was better at escaping immune protection by vaccinations and previous infections.
The reasons for this have so far remained elusive. A new study, published in the journal, 'Cell Research', has shed some light on this topic.
The study, by a research team with scientists from the University of Kent and the Goethe-University Frankfurt showed that Omicron variant viruses are particularly sensitive to inhibition by the so-called interferon response, an unspecific immune response that is present in all body cells. This provided the first explanation of why COVID-19 patients infected with the Omicron variant are less likely to experience severe disease.
The cell culture study also showed that Omicron viruses remained sensitive to eight of the most important antiviral drugs and drug candidates for the treatment of COVID-19. This included EIDD-1931 (active metabolite of molnupiravir), ribavirin, remdesivir, favipravir, PF-07321332 (nirmatrelvir, active ingredient of paxlovid), nafamostat, camostat, and aprotinin.
Prof Martin Michaelis, School of Bioscience, University of Kent, said: "Our study provides for the first time an explanation, why Omicron infections are less likely to cause severe disease. This is due to Omicron, in contrast to Delta, does not effectively inhibit the host cell interferon immune response."
Prof. Jindrich Cinatl, Institute of Medical Virology at the Goethe-University, added: "Although cell culture experiments do not exactly reflect the more complex situation in a patient, our data provide encouraging evidence that the available antiviral COVID-19 drugs are also effective against Omicron."